In the structure of the eye, the retina is present in the eyeground and controls the function of the eye to recognize the presence or absence and shape of an object by the presence of a visual cell layer of the retina. In recent years, patients with eye diseases undergo objective test of retinal function test by the determination of electroretinogram (hereinafter sometimes referred to merely as ERG). This determination is then utilized for the diagnosis of retinal conditions.
The ERG consists of an a-wave, a b-wave, a c-wave and the like. The a-wave is primarily reflects the function of visual cells, the b-wave reflects the function of the bipolar cell layer (mainly Müller cells) and the c-wave reflects the function of the retinal pigment epithelium. When the retinal function is damaged for some reason, it manifests in a change in the peak latency and amplitude of each wave. For example, in the case of diabetic retinopathy, the peak latency of each wave is extended from the early stage and the amplitude is attenuated; in degenerative disease of retina, such as pigmentary retinal degeneration, all waves are attenuated and disappear; and each wave becomes attenuated depending on the stages of disease in retinochoroidal disorders, such as central retinal artery occlusion, central retinal vein thrombosis, fundus hypertonicus, retinal detachment and the like.
While the b-wave originates from the source located more toward the central side of the retina than the visual cell from which the a-wave originates, when the light reaches the retina, the visual cell is first excited and the b-wave and the like are first generated when the excitement is transmitted to the retinal cells on the central side. Therefore, even when the source of origin is other than visual cell, the waves are under strong influence of the function of the visual cell. In other words, when the function of the visual cell is damaged, ERG components become abnormal even if the source of origin of the b-wave and the like is normal. Therefore, in ERG, the a-wave is the most important component, and if changes in peak latency and amplitude of a wave, which are caused by the damaged function of visual cell, can be suppressed or recovered the visual cell function disorder is expected to be effectively treated.